A liquid crystal display device that performs color display typically includes color filters that pass red (R), green (G), and blue (B) light in correspondence with sub-pixels obtained by dividing each pixel into three. Because, however, about two-thirds of backlight radiated onto a liquid crystal display panel is absorbed by the color filters, there is a problem in that the light use efficiency of a liquid crystal display device adopting a color filter method is low. Therefore, liquid crystal display devices adopting a field sequential method, which perform color display without using color filters, are attracting attention.
In the field sequential method, one frame period, which is a period in which one screen is displayed, is divided into three subframe periods. In a first subframe period, a red component of an input signal is input and a red screen is displayed by turning on red light sources. In a second subframe period, a green component is input and a green screen is displayed by turning on green light sources. In a third subframe period, a blue component is input and a blue screen is displayed by turning on blue light sources. As a result, a color image is displayed on a liquid crystal panel. Thus, since color filters are not necessary in a liquid crystal display device adopting the field sequential method, the light use efficiency of a liquid crystal display device adopting the field sequential method is three times as high as that of a liquid crystal display device adopting the color filter method. In addition, because, for example, the number of pixels in a liquid crystal display device adopting the field sequential method can be one-third that in a liquid crystal display device adopting the color filter method, an aperture ratio can be increased.
Now, the optical response speed of liquid crystal is relatively low. Therefore, in a liquid crystal display device adopting the field sequential method, the light transmittance (hereinafter simply referred to as “transmittance”) of liquid crystal at an end of a previous subframe period more or less continues (hereinafter simply referred to as “transmittance continues”) for a while after the subframe period is switched. A subframe period before switching will be referred to as a “preceding subframe period”, and a subframe period after switching, that is, a subframe period immediately after a preceding subframe period, will be referred to as a “succeeding subframe period” herein. If light sources of a color corresponding to a succeeding subframe period are turned on at a beginning of the succeeding subframe period, desired luminance is not achieved because transmittance in a preceding subframe period is continuing. Such a phenomenon is generally called “mixing of colors”.
Therefore, for example, as illustrated in FIG. 6, a method (hereinafter referred to as a “first existing method”) is known in which a timing at which light sources corresponding to each subframe period are turned on is delayed, for example, by a period within which liquid crystal can sufficiently respond while keeping a timing at which the light sources are turned off the same. According to the first existing method, in a period in which transmittance in a preceding subframe continues, which is immediately after the beginning of a succeeding subframe period, light sources of a color corresponding to the succeeding subframe period are not turned on. Therefore, mixing of colors is suppressed. The method illustrated in FIG. 6 is disclosed, for example, in PTL 1, PTL 2, and the like.
In addition, for example, as illustrated in FIG. 7, a method (hereinafter referred to as a “second existing method”) is known in which both the timing at which the light sources corresponding to each subframe period are turned on and the timing at which the light sources are turned off are delayed, for example, by the period within which liquid crystal can sufficiently respond. According to the second existing method, in the period in which transmittance in a preceding subframe period continues, which is immediately after the beginning of a succeeding subframe period, light sources of a color corresponding to the preceding subframe period remain turned on. Therefore, achieved luminance can be close to a desired value. The luminance here corresponds to a time integral of an on period of the light sources of each color and transmittance in the on period. The method illustrated in FIG. 7 is disclosed, for example, in PTL 2 and the like.